1. Field of the Invention
The present invention relates to a sealing structure in a sensor having lead wires such as a brake fluid (oil) level sensor in a vehicle, and more particularly to the sealing structure in which a filling material for the seal is prevented from intruding into a spacing between the lead wires.
2. Description of the Related Art
FIG. 3 shows a sealing structure in a conventional sensor having lead wires. This structure consists of a case 1 formed of a synthetic resin, a reed switch 2 contained in the case 1 and provided with lead wires 3, 4, a rubber plug 19 provided outside the lead wires 3, 4 and fitted to an inner peripheral wall 6a of the case 1, and a resin material 9 filled in an opening 8 of the case 1 above the rubber plug 19 in order to hold the lead wires 3, 4 and seal the reed switch 2.
The reed switch 2 contains therein a pair of magnetic reeds (not shown) whose contact portions are brought into contact by magnetization, and generally employed as a fluid level sensor for a brake or clutch in a vehicle. The sensor 18 having the lead wires is disposed in such a manner that the reed switch 2 faces with a magnetic area in a float (not shown) in an operating fluid such as the brake fluid.
A pair of lead terminals 16, 17 of the reed switch 2 are connected by soldering to conductive terminals 3a, 4a of the lead wires 3, 4 respectively. A pair of the lead wires 3, 4 are passed through bores 13 (FIG. 4) in the rubber plug 19 and guided out of the opening 8 of the case 1 to the connector 11. The connector 11 is composed of a housing 20 formed of a synthetic resin and terminals (not shown) contained in the housing 20. To the terminals are pressure welded distal ends of the lead wires 3, 4.
The case 1 is formed in an oblong shape in cross section, including a bottom portion 14 at one end and the opening 8 at the other end in a longitudinal direction. The opening 8 is enlarged in diameter in a tapered shape. The rubber plug 19 is inserted into the case 1 to be fitted to the inner peripheral face 6a of a cylindrical wall 6 which is straight and continues from the tapered part 8a.
As shown in FIG. 4, at an outer periphery of the rubber plug 19 are formed a plurality of lip portions 12 for tight fitting to the inner peripheral face 6a of the case 1. The bores 13 in the rubber plug 19 are provided slightly apart from each other in a lateral direction so as to correspond to a space between a pair of the lead wires 3, 4. The inner peripheries of the bores 13 are also provided with lip portions (not shown), which are adapted to be tightly fitted to the outer peripheral faces of the lead wires 3, 4.
In FIG. 3, the resin material 9 is filled between an upper end face 19a of the rubber plug 19 and an inlet 8b of the opening 8 of the case 1. The opening 8 covers herein a rather wide area including the inlet 8b and the tapered part 8a which is enlarged in diameter. The resin material 9 which is an epoxy resin or the like will be hardened after poured thereby to hold the lead wires 3, 4 in the case 1, and at the same time, to seal the reed switch 2 and the lead wires 3, 4 inside the case 1. The case 1, the reed switch 2, the lead wires 3, 4, the rubber plug 19 and the resin material 9 constitute the sensor 18 having the lead wires which is the brake fluid level sensor.
The brake fluid level sensor 18 is fixed to a bottom wall of a brake master cylinder (not shown) in the vehicle and may be disposed in the brake fluid, for example. In this case, the rubber plug 19 and the resin material 9 will prevent the brake fluid from intruding into the case 1. In case that the brake fluid level sensor is disposed outside the brake master cylinder, the rubber plug 19 and the resin material 9 will serve for waterproofing or dustproofing purposes.
However, in the above described conventional structure, there has been a problem that when the resin material 9 is poured into the opening 8 of the case 1, the resin material 9 will enter into and rise along a narrow spacing 21 between the lead wires 3, 4 by a capillary phenomenon, as shown in FIG. 3 in an enlarged scale. The resin material 9 thus hardened in this state will create a sharp projection 22 between the lead wires 3, 4, which may damage the coverings on the lead wires 3, 4 when the lead wires 3, 4 are bent at an end face 9a of the resin material 9. This problem may be the same in such a case that a hard rubber material is employed instead of the resin material 9. Particularly, in case where a bending force is applied to the lead wires 3, 4 in filling the resin material 9, the lead wires 3, 4 will be hardened as they are bent and create gaps in the resin material 9, resulting in poor sealing property and deterioration in quality of the products.